The Structure of the Earth-

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Introduction

Planet Earth The Structure of the Earth- The Crust: This region is thin compared to the other layers in the Earth. It varies in thickness from 10km deep to 65km deep. The crust is made up of lighter rocks that "float" on top of the mantle. This layer includes the continents as well as the rock under the oceans. The thickness of the crust might be a little deceiving... to put it into perspective, we have built many deep mines but NONE have yet reached the mantle! The Mantle: This region lies under the crust and is approximately 2900km thick. The mantle is much denser than the crust (which is why the crust floats on top) ...read more.

Middle

Plate tectonics Plate tectonics are a reasonably new theory that has revolutionized the way geologists thinks about the Earth. According to the theory, the surface of the Earth is broken into large plates. The size and position of these plates change over time. The edges of these plates, where they move against each other, this causes earthquakes, volcanoes, and mountain building. Plate tectonics is a combination of two earlier ideas, continental drift and sea-floor spreading. The Earth is made up of several of these different layers. The outer layer is called the Crust. It is made of the lighter, less dense, rocks that floated to the surface when the Earth was formed. The deepest mine in the world is only 3.3km deep, and nobody has ever been able to drill down further than 15km. ...read more.

Conclusion

Continental crust floats on the mantle rather like an iceberg floats in water. There is a balance that exists between the level of the crust and the mantle. If the crust builds up in one area, it will push down on the mantle with more force causing some of the material to move away... this results in another area of the crust being pushed up by the material from that mantle that has been moved away If material is moved off the crust, the mantle pushes up harder causing that area of land to rise and another area (where the material of the mantle came from) to sink. This process goes on constantly and always maintains a balance of downward forces from the crust with the upward forces from the mantle. The proof that they think the earth is made of plates is shown on the picture below. ...read more.

Related AS and A Level Hazardous Environments essays

Even though new oceanic crust is always being formed, old crust is always being destroyed, and so there is no very ancient oceanic rock around. If this didn't happen, the world would have to be constanly expanding to make way for the extra crust being formed!

As it does so volcanoes are produced all along the Andes some of which are still active to this day. Here are two examples of diverging plates. Where rising convection currents spread sideways beneath the crust they pull the plates apart and the molten basalt is forced upwards from the